A microlithographic lens is a high resolution lens used in the manufacture of semiconductor devices. The microlithographic objective lens forms images carried by light propagating from a reticle illuminated by a laser and incident on a silicon wafer coated with a photoresist material. State of the art lithographic optical systems use a 193 nm ArF excimer laser to illuminate the reticle. A high resolution microlithographic objective lens ideally causes fractional magnification of the image carried by the light in the absence of significant image-distorting aberrations to form an image in fine detail. The formation of images in fine detail enables the manufacture of high density semiconductor devices. High resolution lens performance can be achieved by one or both of decreasing the wavelength of image-carrying light and increasing the numerical operature (NA) of the objective lens.
Calcium fluoride is a crystalline material typically used in the manufacture of lens components of 193 nm lithography tools. Intrinsic birefringence of calcium fluoride crystal material presents a serious threat to the optical performance of very high NA 157 nm lithography tools. What is needed, therefore, is a high resolution objective lens that is formed with optical components made from alternative refractive lens materials that degrade to a lesser degree the optical performance of the tool in which the lens is incorporated.